Encapsulated cathode active material particles, lithium secondary batteries containing same, and method of manufacturing

ABSTRACT

Provided is particulate of a cathode active material for a lithium battery, comprising one or a plurality of cathode active material particles being embraced or encapsulated by a thin layer of a high-elasticity polymer having a recoverable tensile strain no less than 5%, a lithium ion conductivity no less than 10 −6  S/cm at room temperature, and a thickness from 0.5 nm to 10 μm, wherein the polymer contains an ultrahigh molecular weight (UHMW) polymer having a molecular weight from 0.5×10 6  to 9×10 6  grams/mole. The UHMW polymer is preferably selected from polyacrylonitrile, polyethylene oxide, polypropylene oxide, polyethylene glycol, polyvinyl alcohol, polyacrylamide, poly(methyl methacrylate), poly(methyl ether acrylate), a copolymer thereof, a sulfonated derivative thereof, a chemical derivative thereof, or a combination thereof.

FIELD OF THE INVENTION

The present invention relates generally to the field of rechargeablelithium battery and, more particularly, to the lithium battery cathodeactive material, cathode layer, and battery cell, and a method ofmanufacturing same.

BACKGROUND OF THE INVENTION

A unit cell or building block of a lithium-ion battery is typicallycomposed of an anode current collector, an anode or negative electrodelayer (containing an anode active material responsible for storinglithium therein, a conductive additive, and a resin binder), anelectrolyte and porous separator, a cathode or positive electrode layer(containing a cathode active material responsible for storing lithiumtherein, a conductive additive, and a resin binder), and a separatecathode current collector. The electrolyte is in ionic contact with boththe anode active material and the cathode active material. A porousseparator is not required if the electrolyte is a solid-stateelectrolyte.

The binder in the anode layer is used to bond the anode active material(e.g. graphite or Si particles) and a conductive filler (e.g. carbonblack particles or carbon nanotube) together to form an anode layer ofstructural integrity, and to bond the anode layer to a separate anodecurrent collector, which acts to collect electrons from the anode activematerial when the battery is discharged. In other words, in the negativeelectrode (anode) side of the battery, there are typically fourdifferent materials involved: an anode active material, a conductiveadditive, a resin binder (e.g. polyvinylidine fluoride, PVDF, orstyrene-butadiene rubber, SBR), and an anode current collector(typically a sheet of Cu foil). Typically the former three materialsform a separate, discrete anode active material layer (or, simply, anodelayer) and the latter one forms another discrete layer (currentcollector layer).

A binder resin (e.g. PVDF or PTFE) is also used in the cathode to bondcathode active materials and conductive additive particles together toform a cathode active layer of structural integrity. The same resinbinder also acts to bond this cathode active layer to a cathode currentcollector (e.g. Al foil).

Historically, lithium-ion batteries actually evolved from rechargeable“lithium metal batteries” that use lithium (Li) metal as the anode and aLi intercalation compound (e.g. MoS₂) as the cathode. Li metal is anideal anode material due to its light weight (the lightest metal), highelectronegativity (−3.04 V vs. the standard hydrogen electrode), andhigh theoretical capacity (3,860 mAh/g). Based on these outstandingproperties, lithium metal batteries were proposed 40 years ago as anideal system for high energy-density applications.

Due to some safety concerns (e.g. lithium dendrite formation andinternal shorting) of pure lithium metal, graphite was implemented as ananode active material in place of the lithium metal to produce thecurrent lithium-ion batteries. The past two decades have witnessed acontinuous improvement in Li-ion batteries in terms of energy density,rate capability, and safety. However, the use of graphite-based anodesin Li-ion batteries has several significant drawbacks: low specificcapacity (theoretical capacity of 372 mAh/g as opposed to 3,860 mAh/gfor Li metal), long Li intercalation time (e.g. low solid-statediffusion coefficients of Li in and out of graphite and inorganic oxideparticles) requiring long recharge times (e.g. 7 hours for electricvehicle batteries), inability to deliver high pulse power (power density<0.5 kW/kg), and necessity to use pre-lithiated cathodes (e.g. lithiumcobalt oxide, as opposed to cobalt oxide), thereby limiting the choiceof available cathode materials.

Further, these commonly used cathode active materials have a relativelylow specific capacity (typically <220 mAh/g). These factors havecontributed to the two major shortcomings of today's Li-ion batteries—alow energy density (typically 150-220 Wh/kg_(cell)) and low powerdensity (typically <0.5 kW/kg). In addition, even though the lithiummetal anode has been replaced by an intercalation compound (e.g.graphite) and, hence, there is little or no lithium dendrite issue inthe lithium-ion battery, the battery safety issue has not gone away.There have been no short of incidents involving lithium-ion batteriescatching fire or exploding. To sum it up, battery scientists have beenfrustrated with the low energy density, inadequate cycle life, andflammability of lithium-ion cells for over three decades!

There have been tremendous efforts made in battery industry and researchcommunity to improve existing cathode materials and develop new cathodecompositions. However, current and emerging cathode active materials forlithium secondary batteries still suffer from the following seriousdrawbacks:

-   -   (1) The most commonly used cathode active materials (e.g.        lithium transition metal oxides) contain a transition metal        (e.g. Fe, Mn, Co, Ni, etc.) that is a powerful catalyst that can        promote undesirable chemical reactions inside a battery (e.g.        decomposition of electrolyte). These cathode active materials        also contain a high oxygen content that could assist in the        progression of thermal runaway and provide oxygen for        electrolyte oxidation, increasing the danger of explosion or        fire hazard. This is a serious problem that has hampered the        widespread implementation of electric vehicles.    -   (2) Most of promising organic or polymeric cathode active        materials are either soluble in the commonly used electrolytes        or are reactive with these electrolytes. Dissolution of active        material in the electrolyte results in a continuing loss of the        active material. Undesirable reactions between the active        material and the electrolyte lead to graduate depletion of the        electrolyte and the active material in the battery cell. All        these phenomena lead to capacity loss of the battery and        shortened cycle life.    -   (3) The practical capacity achievable with current cathode        materials (e.g. lithium iron phosphate and lithium transition        metal oxides) has been limited to the range of 150-250 mAh/g        and, in most cases, less than 200 mAh/g. Additionally, emerging        high-capacity cathode active materials (e.g. FeF₃) still cannot        deliver a long battery cycle life.        -   High-capacity cathode active materials, such as metal            fluoride, metal chloride, and lithium transition metal            silicide, can undergo large volume expansion and shrinkage            during the discharge and charge of a lithium battery. These            repeated volume changes lead to structural instability of            the cathode, breakage of the normally weak bond between the            binder resin and the active material, fragmentation of            active material particles, delamination between the cathode            active material layer and the current collector, and            interruption of electron-conducting pathways. These            high-capacity cathodes include CoF₃, MnF₃, FeF₃, VF₃, VOF₃,            TiF₃, BiF₃, NiF₂, FeF₂, CuF₂, CuF, SnF₂, AgF, CuCl₂, FeCl₃,            MnCl₂, etc. High-capacity cathode active materials also            include a lithium transition metal silicate, Li₂MSiO₄ or            Li₂Ma_(x)Mb_(y)SiO₄, wherein M and Ma are selected from Fe,            Mn, Co, Ni, V, or VO; Mb is selected from Fe, Mn, Co, Ni, V,            Ti, Al, B, Sn, or Bi; and x+y≤1.

Hence, there is an urgent and continuing need for a new cathode activematerial and a cathode active material layer that enable a lithiumsecondary battery to deliver a long cycle life and higher energydensity. There is also a need for a method of readily and easilyproducing such a material in large quantities. Thus, it is a primaryobject of the present invention to meet these needs and address theissues associated the rapid capacity decay of a lithium battery.

SUMMARY OF THE INVENTION

Herein reported is a cathode active material layer for a lithium batterythat contains a very unique class of cathode active material.Specifically, the cathode active material particles are fully embracedor encapsulated by a high-elasticity polymer (containing an ultra-highmolecular weight polymer) that is capable of overcoming thecathode-induced rapid capacity decay problem commonly associated with arechargeable lithium battery.

The instant invention is directed at a lithium-ion battery (using alithium intercalation compound or conversion-type compound, not lithiummetal, as the anode active material) or a lithium metal battery (usinglithium metal as the anode active material and a lithium intercalationor conversion compound as the cathode active material, but not includingsulfur or alkali metal polysulfide). Both alkali metal-sulfur cells(Li—S, Na—S, and K—S) and the lithium-air cell are excluded from theclaims of instant application.

In a preferred embodiment, the invention provides a cathode activematerial particulate for a lithium battery, preferably a rechargeablebattery. The cathode active material particulate is composed of one or aplurality of cathode active material particles being fully embraced orencapsulated by a thin layer of a high-elasticity polymer (containing anultra-high molecular weight polymer) having a recoverable tensile strainfrom 5% to 200% when measured without an additive or reinforcement, alithium ion conductivity no less than 10⁻⁶ S/cm at room temperature, anda thickness from 0.5 nm to 10 μm. When measured with an additive orreinforcement in the polymer, the tensile elastic deformation of theresulting composite must remain greater than 2%. The polymer also has alithium ion conductivity no less than 10⁻⁶ S/cm at room temperature(preferably and more typically no less than 10⁻⁴ S/cm and morepreferably and typically no less than 10⁻³ S/cm).

The ultrahigh molecular weight (UHMW) polymer is preferably selectedfrom polyacrylonitrile (PAN), polyethylene oxide (PEO), polypropyleneoxide (PPO), polyethylene glycol (PEG), polyvinyl alcohol (PVA),polyacrylamide (PAA), poly(methyl methacrylate) (PMMA), poly(methylether acrylate) (PMEA), a copolymer thereof, a sulfonated derivativethereof, a chemical derivative thereof, or a combination thereof.

Preferably, the particulates are substantially or essentially sphericalor ellipsoidal in shape. Also preferably, the particulate have adiameter or thickness smaller than 30 μm, more preferably smaller than20 μm, and most preferably smaller than 10 μm.

High-elasticity polymer refers to a polymer that exhibits an elasticdeformation of at least 2% (preferably at least 5%) when measured underuniaxial tension. In the field of materials science and engineering, the“elastic deformation” is defined as a deformation of a material (whenbeing mechanically stressed) that is essentially fully recoverable uponrelease of the load and the recovery process is essentiallyinstantaneous (no or little time delay). Conventionally, such a highelasticity comes from a lightly cross-linked polymer or rubber. Incontrast, the instant high-elasticity polymer comes from a thermoplasticpolymer (a non-cross-linked polymer or a polymer containing nocross-linked network). This thermoplastic is not a cross-linked polymer.The elastic deformation of instant UHMW polymer is typically andpreferably greater than 10%, more preferably greater than 30%, furthermore preferably greater than 50%, and still more preferably greater than100%.

The UHMW polymer preferably has a molecular weight from 0.5×10⁶ to lessthan 5×10⁶ grams/mole, more preferably from 1×10⁶ to less than 3×10⁶grams/mole for ease of particulate production. The UHMW polymer can havea molecular weight higher than 5×10⁶ g/mole, or even up to 9×10⁶ g/mole.Too high a molecular weight can make it difficult to deposit a thinembracing polymer layer around an active material particle.

In certain embodiments, the ultrahigh molecular weight polymer containsan electrically conductive material dispersed therein. The electricallyconducting material may be selected from an electron-conducting polymer,a metal particle or wire, a graphene sheet, a carbon fiber, a graphitefiber, a carbon nano-fiber, a graphite nano-fiber, a carbon nanotube, agraphite particle, an expanded graphite flake, an acetylene blackparticle, or a combination thereof. The electrically conducting material(e.g. metal nano-wire, nano-fiber, etc.) preferably has a thickness ordiameter less than 100 nm.

In certain embodiments, the ultrahigh molecular weight polymer containsa lithium salt and/or a liquid solvent dispersed between chains of theultrahigh molecular weight polymer.

The liquid solvent dispersed in the UHMW polymer may be preferablyselected from 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME),tetraethylene glycol dimethylether (TEGDME), poly(ethylene glycol)dimethyl ether (PEGDME), diethylene glycol dibutyl ether (DEGDBE),2-ethoxyethyl ether (EEE), sulfone, sulfolane, ethylene carbonate (EC),propylene carbonate (PC), dimethyl carbonate (DMC), methylethylcarbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methylpropionate, gamma-butyrolactone (γ-BL), acetonitrile (AN), ethyl acetate(EA), propyl formate (PF), methyl formate (MF), toluene, xylene, methylacetate (MA), fluoroethylene carbonate (FEC), vinylene carbonate (VC),allyl ethyl carbonate (AEC), a hydrofluoroether, an ionic liquidsolvent, or a combination thereof

The lithium salt dispersed in the UHMW polymer may be preferablyselected from lithium perchlorate (LiClO₄), lithium hexafluorophosphate(LiPF₆), lithium borofluoride (LiBF₄), lithium hexafluoroarsenide(LiAsF₆), lithium trifluoro-metasulfonate (LiCF₃SO₃),bis-trifluoromethyl sulfonylimide lithium (LiN(CF₃SO₂)₂), lithiumbis(oxalato)borate(LiBOB), lithium oxalyldifluoroborate (LiBF₂C₂O₄),lithium oxalyldifluoroborate (LiBF₂C₂O₄), lithium nitrate (LiNO₃),Li-Fluoroalkyl-Phosphates (LiPF₃(CF₂CF₃)₃), lithiumbisperfluoro-ethysulfonylimide (LiBETI), lithiumbis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide,lithium trifluoromethanesulfonimide (LiTFSI), an ionic liquid-basedlithium salt, or a combination thereof.

The cathode active material particulate may contain a cathode activematerial selected from an inorganic material, an organic material, apolymeric material, or a combination thereof. The inorganic material maybe selected from a metal oxide, metal phosphate, metal silicide, metalselenide, transition metal sulfide, or a combination thereof. Theinorganic material does not include sulfur or alkali metal polysulfide.

The inorganic material may be selected from a lithium cobalt oxide,lithium nickel oxide, lithium manganese oxide, lithium vanadium oxide,lithium-mixed metal oxide, lithium iron phosphate, lithium manganesephosphate, lithium vanadium phosphate, lithium mixed metal phosphate,lithium metal silicide, or a combination thereof.

In certain preferred embodiments, the inorganic material is selectedfrom a metal fluoride or metal chloride including the group consistingof CoF₃, MnF₃, FeF₃, VF₃, VOF₃, TiF₃, BiF₃, NiF₂, FeF₂, CuF₂, CuF, SnF₂,AgF, CuCl₂, FeCl₃, MnCl₂, and combinations thereof. In certain preferredembodiments, the inorganic material is selected from a lithiumtransition metal silicate, denoted as Li₂MSiO₄ or Li₂Ma_(x)Mb_(y)SiO₄,wherein M and Ma are selected from Fe, Mn, Co, Ni, V, or VO; Mb isselected from Fe, Mn, Co, Ni, V, Ti, Al, B, Sn, or Bi; and x+y≤1.

In certain preferred embodiments, the inorganic material is selectedfrom a transition metal dichalcogenide, a transition metaltrichalcogenide, or a combination thereof. The inorganic material isselected from TiS₂, TaS₂, MoS₂, NbSe₃, MnO₂, CoO₂, an iron oxide, avanadium oxide, or a combination thereof.

The cathode active material layer may contain a metal oxide containingvanadium oxide selected from the group consisting of VO₂, Li_(x)VO₂,V₂O₅, Li_(x)V₂O₅, V₃O₈, Li_(x)V₃O₈, Li_(x)V₃O₇, V₄O₉, Li_(x)V₄O₉, V₆O₁₃,Li_(x)V₆O₁₃, their doped versions, their derivatives, and combinationsthereof, wherein 0.1<x<5.

The cathode active material layer may contain a metal oxide or metalphosphate, selected from a layered compound LiMO₂, spinel compoundLiM₂O₄, olivine compound LiMPO₄, silicate compound Li₂MSiO₄, Tavoritecompound LiMPO₄F, borate compound LiMBO₃, or a combination thereof,wherein M is a transition metal or a mixture of multiple transitionmetals.

In some embodiments, the inorganic material is selected from: (a)bismuth selenide or bismuth telluride, (b) transition metaldichalcogenide or trichalcogenide, (c) sulfide, selenide, or tellurideof niobium, zirconium, molybdenum, hafnium, tantalum, tungsten,titanium, cobalt, manganese, iron, nickel, or a transition metal; (d)boron nitride, or (e) a combination thereof.

The cathode active material layer may contain an organic material orpolymeric material selected from Poly(anthraquinonyl sulfide) (PAQS), alithium oxocarbon, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),poly(anthraquinonyl sulfide), pyrene-4,5,9,10-tetraone (PYT),polymer-bound PYT, Quino(triazene), redox-active organic material,Tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE),2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), poly(5-amino-1,4-dyhydroxyanthraquinone) (PADAQ), phosphazene disulfide polymer ([(NPS₂)₃]n),lithiated 1,4,5,8-naphthalenetetraol formaldehyde polymer,Hexaazatrinaphtylene (HATN), Hexaazatriphenylene hexacarbonitrile(HAT(CN)₆), 5-Benzylidene hydantoin, Isatine lithium salt, Pyromelliticdiimide lithium salt, tetrahydroxy-p-benzoquinone derivatives (THQLi₄),N,N′-diphenyl-2,3,5,6-tetraketopiperazine (PHP),N,N′-diallyl-2,3,5,6-tetraketopiperazine (AP),N,N′-dipropyl-2,3,5,6-tetraketopiperazine (PRP), a thioether polymer, aquinone compound, 1,4-benzoquinone, 5,7,12,14-pentacenetetrone (PT),5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ),5-amino-1,4-dyhydroxy anthraquinone (ADAQ), calixquinone, Li₄C₆O₆,Li₂C₆O₆, Li₆C₆O₆, or a combination thereof.

The thioether polymer is selected fromPoly[methanetetryl-tetra(thiomethylene)] (PMTTM),Poly(2,4-dithiopentanylene) (PDTP), a polymer containingPoly(ethene-1,1,2,2-tetrathiol) (PETT) as a main-chain thioetherpolymers, a side-chain thioether polymer having a main-chain consistingof conjugating aromatic moieties, and having a thioether side chain as apendant, Poly(2-phenyl-1,3-dithiolane) (PPDT),Poly(1,4-di(1,3-dithiolan-2-yl)benzene) (PDDTB),poly(tetrahydrobenzodithiophene) (PTHBDT),poly[1,2,4,5-tetrakis(propylthio)benzene] (PTKPTB, orpoly[3,4(ethylenedithio)thiophene] (PEDTT).

In other embodiments, the cathode active material layer contains anorganic material selected from a phthalocyanine compound, such as copperphthalocyanine, zinc phthalocyanine, tin phthalocyanine, ironphthalocyanine, lead phthalocyanine, nickel phthalocyanine, vanadylphthalocyanine, fluorochromium phthalocyanine, magnesium phthalocyanine,manganous phthalocyanine, dilithium phthalocyanine, aluminumphthalocyanine chloride, cadmium phthalocyanine, chlorogalliumphthalocyanine, cobalt phthalocyanine, silver phthalocyanine, ametal-free phthalocyanine, a chemical derivative thereof, or acombination thereof.

The cathode active material is preferably in a form of nano particle(spherical, ellipsoidal, and irregular shape), nano wire, nano fiber,nano tube, nano sheet, nano belt, nano ribbon, nano disc, nano platelet,or nano horn having a thickness or diameter less than 100 nm. Theseshapes can be collectively referred to as “particles” unless otherwisespecified or unless a specific type among the above species is desired.Further preferably, the cathode active material has a dimension lessthan 50 nm, even more preferably less than 20 nm, and most preferablyless than 10 nm.

In some embodiments, one particle or a cluster of particles may becoated with or embraced by a layer of carbon disposed between theparticle(s) and the high-elasticity polymer layer (the encapsulatingshell). Alternatively or additionally, a carbon layer may be depositedto embrace the encapsulated particle or the encapsulated cluster ofmultiple cathode active material particles.

The particulate may further contain a graphite, graphene, or carbonmaterial mixed with the cathode active material particles and disposedinside the encapsulating or embracing polymer shell. The carbon orgraphite material is selected from polymeric carbon, amorphous carbon,chemical vapor deposition carbon, coal tar pitch, petroleum pitch,meso-phase pitch, carbon black, coke, acetylene black, activated carbon,fine expanded graphite particle with a dimension smaller than 100 nm,artificial graphite particle, natural graphite particle, or acombination thereof. Graphene may be selected from pristine graphene,graphene oxide, reduced graphene oxide, graphene fluoride, hydrogenatedgraphene, nitrogenated graphene, functionalized graphene, etc.

The cathode active material particles may be coated with or embraced bya conductive protective coating, selected from a carbon material,graphene, electronically conductive polymer, conductive metal oxide, orconductive metal coating. Preferably, the cathode active material, inthe form of a nano particle, nano wire, nano fiber, nano tube, nanosheet, nano belt, nano ribbon, nano disc, nano platelet, or nano horn ispre-intercalated or pre-doped with lithium ions to form a prelithiatedanode active material having an amount of lithium from 0.1% to 54.7% byweight of said prelithiated anode active material.

Preferably and typically, the high-elasticity polymer has a lithium ionconductivity no less than 10⁻⁵ S/cm, more preferably no less than 10⁻³S/cm, and most preferably no less than 10⁻² S/cm. Some of the selectedpolymers exhibit a lithium-ion conductivity greater than 10⁻² S/cm. Insome embodiments, the high-elasticity polymer is a neat UHMW polymercontaining no additive or filler dispersed therein. In others, thehigh-elasticity polymer is polymer matrix composite containing from 0.1%to 50% by weight (preferably from 1% to 35% by weight) of a lithiumion-conducting additive dispersed in an UHMW polymer matrix material. Insome embodiments, the high-elasticity polymer contains from 0.1% byweight to 10% by weight of a reinforcement nano filament selected fromcarbon nanotube, carbon nano-fiber, graphene, or a combination thereof.

In some embodiments, the UHMW polymer is mixed with an elastomer (toform a blend, co-polymer, or interpenetrating network) selected fromnatural polyisoprene (e.g. cis-1,4-polyisoprene natural rubber (NR) andtrans-1,4-polyisoprene gutta-percha), synthetic polyisoprene (IR forisoprene rubber), polybutadiene (BR for butadiene rubber), chloroprenerubber (CR), polychloroprene (e.g. Neoprene, Baypren etc.), butyl rubber(copolymer of isobutylene and isoprene, IIR), including halogenatedbutyl rubbers (chloro butyl rubber (CIIR) and bromo butyl rubber (BIIR),styrene-butadiene rubber (copolymer of styrene and butadiene, SBR),nitrile rubber (copolymer of butadiene and acrylonitrile, NBR), EPM(ethylene propylene rubber, a copolymer of ethylene and propylene), EPDMrubber (ethylene propylene diene rubber, a terpolymer of ethylene,propylene and a diene-component), epichlorohydrin rubber (ECO),polyacrylic rubber (ACM, ABR), silicone rubber (SI, Q, VMQ),fluorosilicone rubber (FVMQ), fluoroelastomers (FKM, and FEPM; such asViton, Tecnoflon, Fluorel, Aflas and Dai-E1), perfluoroelastomers (FFKM:Tecnoflon PFR, Kalrez, Chemraz, Perlast), polyether block amides (PEBA),chlorosulfonated polyethylene (CSM; e.g. Hypalon), and ethylene-vinylacetate (EVA), thermoplastic elastomers (TPE), protein resilin, proteinelastin, ethylene oxide-epichlorohydrin copolymer, polyurethane,urethane-urea copolymer, and combinations thereof.

In some embodiments, the high-elasticity polymer is a compositecontaining a lithium ion-conducting additive dispersed in an UHMWpolymer matrix material, wherein the lithium ion-conducting additive isselected from Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi,(ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y), or a combination thereof,wherein X=F, Cl, I, or Br, R=a hydrocarbon group, x=0-1, y=1-4.

The UHMW polymer may form a mixture, blend, co-polymer, orsemi-interpenetrating network (semi-IPN) with an electron-conductingpolymer selected from polyaniline, polypyrrole, polythiophene,polyfuran, a bi-cyclic polymer, derivatives thereof (e.g. sulfonatedversions), or a combination thereof.

In some embodiments, the UHMW polymer may form a mixture, blend, orsemi-IPN with a lithium ion-conducting polymer selected frompoly(ethylene oxide) (PEO), Polypropylene oxide (PPO),poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA),poly(vinylidene fluoride) (PVdF), Poly bis-methoxyethoxyethoxide-phosphazenex, Polyvinyl chloride, Polydimethylsiloxane,poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a sulfonatedderivative thereof, or a combination thereof. Sulfonation is hereinfound to impart improved lithium ion conductivity to a polymer.

The present invention also provides a cathode electrode that containsthe presently invented high-elasticity polymer-encapsulated cathodeactive material particles, and an optional conductive additive (e.g.expanded graphite flakes, carbon black, acetylene black, or carbonnanotube), an optional resin binder (typically required).

The present invention also provides a lithium battery containing anoptional anode current collector, an anode active material layer, aninvented cathode active material layer as described above, an optionalcathode current collector, an electrolyte in ionic contact with theanode active material layer and the cathode active material layer and anoptional porous separator. The lithium battery may be a lithium-ionbattery or lithium metal battery (containing lithium metal or lithiumalloy as the main anode active material and containing nointercalation-based anode active material), including lithium-seleniumbattery, but excluding alkali metal-sulfur battery and lithium-airbattery for defining the claims.

The present invention also provides a method of manufacturing a lithiumbattery. The method includes (a) providing a cathode active materiallayer and an optional cathode current collector to support the cathodeactive material layer; (b) providing an anode active material layer andan optional anode current collector to support the anode active materiallayer; and (c) providing an electrolyte in contact with the anode activematerial layer and the cathode active material layer and an optionalseparator electrically isolating (separating) the anode and the cathode;wherein the operation of providing the cathode active material layerincludes fully embracing or encapsulating particles of a cathode activematerial by a high-elasticity polymer (containing an ultra-highmolecular weight polymer) to form protected particulates, wherein thehigh-elasticity polymer has a recoverable tensile elastic strain from 2%to 200% (preferably >5% when measured without an additive orreinforcement), a lithium ion conductivity no less than 10⁻⁶ S/cm atroom temperature, and a thickness from 0.5 nm to 10 μm (preferably from1 to 100 nm).

This high-elasticity polymer encapsulation layer appears to be capableof isolating (preventing) liquid electrolyte from being in directphysical contact with the cathode active material and, thus, preventingthe catalytic elements (e.g. Fe, Mn, Ni, Co, etc.) in the cathode activematerial from catalyzing the decomposition of the electrolyte. Thisotherwise could cause fast capacity decay and fire and explosion hazard.This high-elasticity polymer encapsulation layer also preventsdissolution of an organic or polymeric active material in the liquidelectrolyte, which otherwise would lead to continuing loss of the activematerial and, thus, loss in capacity.

Preferably, the high-elasticity polymer has a lithium ion conductivityfrom 1×10⁻⁵ S/cm to 5×10⁻² S/cm. In some embodiments, thehigh-elasticity polymer has a recoverable tensile strain from 10% to200% (more preferably >30%, and further more preferably >50%).

In certain embodiments, the operation of providing a high-elasticitypolymer contains providing a mixture/blend/composite of an ultra-highmolecular weight polymer with an elastomer, an electronically conductivepolymer (e.g. polyaniline, polypyrrole, polythiophene, polyfuran, abi-cyclic polymer, a sulfonated derivative thereof, or a combinationthereof), a lithium-ion conducting material, a reinforcement material(e.g. carbon nanotube, carbon nano-fiber, and/or graphene), or acombination thereof.

In this mixture/blend/composite, the lithium ion-conducting material isdispersed in the high-elasticity polymer and is preferably selected fromLi₂CO₃, Li₂O, Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂,(CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y), or a combination thereof, wherein X=F,Cl, I, or Br, R=a hydrocarbon group, x=0−1, y=1−4.

In some embodiments, the lithium ion-conducting material is dispersed inthe high-elasticity polymer and is selected from lithium perchlorate,LiClO₄, lithium hexafluorophosphate, LiPF₆, lithium borofluoride, LiBF₄,lithium hexafluoroarsenide, LiAsF₆, lithium trifluoro-metasulfonate,LiCF₃SO₃, bis-trifluoromethyl sulfonylimide lithium, LiN(CF₃SO₂)₂,lithium bis(oxalato)borate, LiBOB, lithium oxalyldifluoroborate,LiBF₂C₂O₄, lithium oxalyldifluoroborate, LiBF₂C₂O₄, lithium nitrate,LiNO₃, Li-Fluoroalkyl-Phosphates, LiPF₃(CF₂CF₃)₃, lithiumbisperfluoro-ethysulfonylimide, LiBETI, lithiumbis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide,lithium trifluoromethanesulfonimide, LiTFSI, an ionic liquid-basedlithium salt, or a combination thereof.

Preferably, the cathode active material particles are coated with alayer of carbon or graphene prior to being embraced by thehigh-elasticity polymer. Preferably, cathode active material particlesand particles of a carbon or graphite material are bonded together bythe high-elasticity polymer. Preferably, the cathode active materialparticles, possibly along with a carbon or graphite material and/or withsome internal graphene sheets, are embraced by graphene sheets to formcathode active material particulates, which are then encapsulated by thehigh-elasticity polymer. The graphene sheets may be selected frompristine graphene (e.g. that prepared by CVD or liquid phase exfoliationusing direct ultrasonication), graphene oxide, reduced graphene oxide(RGO), graphene fluoride, doped graphene, functionalized graphene, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) Schematic of a prior art lithium-ion battery cell, wherein theanode layer is a thin coating of an anode active material (Li orlithiated Si) and the cathode is composed of particles of a cathodeactive material, a conductive additive (not shown) and a resin binder(not shown).

FIG. 1(B) Schematic of another prior art lithium-ion battery; the anodelayer being composed of particles of an anode active material, aconductive additive (not shown) and a resin binder (not shown).

FIG. 2(A) Schematic illustrating the notion that expansion/shrinkage ofelectrode active material particles, upon lithium insertion andde-insertion during discharge/charge of a prior art lithium-ion battery,can lead to detachment of resin binder from the particles, interruptionof the conductive paths formed by the conductive additive, and loss ofcontact with the current collector;

FIG. 2(B) Several different types of particulates containinghigh-elasticity polymer encapsulated cathode active material particles.

FIG. 3(A) The representative tensile stress-strain curve of an UHMWPEO-EC polymer.

FIG. 3(B) The specific intercalation capacity curves of four lithiumcells: cathode containing un-encapsulated V₂O₅ particles, cathodecontaining un-encapsulated but graphene-embraced V₂O₅ particles, cathodecontaining UHMW PEO-encapsulated V₂O₅ particles, and cathode containingUHMW PEO-encapsulated graphene-embraced V₂O₅ particles.

FIG. 4(A) Representative tensile stress-strain curves of UHMW PAN/PCpolymer film.

FIG. 4(B) The specific capacity values of two lithium battery cellshaving a cathode active material featuring (1) high-elasticity UHMWPAN/PC-encapsulated carbon-coated LiFePO₄ particles and (2)carbon-coated LiFePO₄ particles without polymer encapsulation,respectively.

FIG. 5 The discharge capacity curves of two coin cells having twodifferent types of cathode active materials: (1) high-elasticity UHMWPPO-encapsulated metal fluoride particles and (2) non-encapsulated metalfluorides.

FIG. 6 Specific capacities of two lithium-FePc (organic) cells, eachhaving Li as an anode active material and FePc/RGO mixture particles asthe cathode active material (one cell containing un-encapsulatedparticles and the other containing particles encapsulated by UHMW PANpolymer).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention is directed at the cathode active material layer(positive electrode layer, not including the cathode current collector)containing a cathode active material in a protected particulate form fora lithium secondary battery, which is preferably a secondary batterybased on a non-aqueous electrolyte, a polymer gel electrolyte, an ionicliquid electrolyte, a quasi-solid electrolyte, or a solid-stateelectrolyte. The shape of a lithium secondary battery can becylindrical, square, button-like, etc. The present invention is notlimited to any battery shape or configuration or any type ofelectrolyte. The invention also provides such a protected cathodeparticulate composed of cathode active material particles encapsulatedor embraced by a thin layer of a high-elasticity polymer containing anultra-high molecular weight polymer.

As illustrated in FIG. 1(B), a lithium-ion battery cell is typicallycomposed of an anode current collector (e.g. Cu foil), an anode ornegative electrode active material layer (i.e. anode layer typicallycontaining particles of an anode active material, conductive additive,and binder), a porous separator and/or an electrolyte component, acathode or positive electrode active material layer (containing acathode active material, conductive additive, and resin binder), and acathode current collector (e.g. Al foil). More specifically, the anodelayer is composed of particles of an anode active material (e.g.graphite, Sn, SnO₂, or Si), a conductive additive (e.g. carbon blackparticles), and a resin binder (e.g. SBR or PVDF). This anode layer istypically 50-300 μm thick (more typically 100-200 μm) to give rise to asufficient amount of current per unit electrode area. Similarly, thecathode layer is composed of particles of a cathode active material(e.g. LiCoO₂, LiMnO₄, LiFePO₄, etc.), a conductive additive (e.g. carbonblack particles), and a resin binder (e.g. PVDF or PTFE). This cathodelayer is typically 100-300 μm thick.

In a lithium metal cell, as illustrated in FIG. 1(A), the anode activematerial is deposited in a thin film form or a thin foil form directlyonto an anode current collector. If a layer of Li coating or Li foil isused as the anode active material, the battery is a lithium metalbattery, lithium sulfur battery, lithium-air battery, lithium-seleniumbattery, etc.

In order to obtain a higher energy density lithium-ion cell, the anodein FIG. 1(B) can be designed to contain higher-capacity anode activematerials having a composition formula of Li_(a)A (A is a metal orsemiconductor element, such as Al and Si, and “a” satisfies 0<a≤5).These materials are of great interest due to their high theoreticalcapacity, e.g., Li₄Si (3,829 mAh/g), Li_(4.4)Si (4,200 mAh/g),Li_(4.4)Ge (1,623 mAh/g), Li_(4.4)Sn (993 mAh/g), Li₃Cd (715 mAh/g),Li₃Sb (660 mAh/g), Li_(4.4)Pb (569 mAh/g), LiZn (410 mAh/g), and Li₃Bi(385 mAh/g).

As schematically illustrated in FIG. 2(A), one major problem in thecurrent lithium battery is the notion that active material particles canget fragmented and the binder resin can detach from both the activematerial particles and conductive additive particles due to volumeexpansion/shrinkage of the active material particles during the chargeand discharge cycles. These binder detachment and particle fragmentationphenomena lead to loss of contacts between active material particles andconductive additives and loss of contacts between the anode activematerial and its current collector. These adverse effects result in asignificantly shortened charge-discharge cycle life.

We have solved these challenging issues that have troubled batterydesigners and electrochemists alike for more than 30 years by developinga new class of cathode active materials. The cathode active materiallayer comprises multiple cathode active material particles that arefully embraced or encapsulated by a high-elasticity polymer (containingan UHMW polymer) having a recoverable (elastic) tensile strain no lessthan 2% under uniaxial tension and a lithium ion conductivity no lessthan 10⁻⁶ S/cm at room temperature (preferably and more typically from1×10⁻⁵ S/cm to 5×10⁻² S/cm).

As illustrated in FIG. 2(B), the present invention provides four majortypes of particulates of high-elasticity polymer-encapsulated cathodeactive material particles. The first one is a single-particleparticulate containing a cathode active material core 10 encapsulated bya high-elasticity polymer shell 12. The second is a multiple-particleparticulate containing multiple cathode active material particles 14(e.g. FeF₃ particles), optionally along with other conductive materials(e.g. particles of graphite or hard carbon, not shown), which areencapsulated by a high-elasticity polymer 16. The third is asingle-particle particulate containing a cathode active material core 18coated by a carbon or graphene layer 20 (or other conductive material)further encapsulated by a high-elasticity polymer 22. The fourth is amultiple-particle particulate containing multiple cathode activematerial particles 24 (e.g. FeF₃ particles) coated with a conductiveprotection layer 26 (carbon, graphene, etc.), optionally along withother active materials or conductive additive, which are encapsulated bya high-elasticity polymer shell 28.

High-elasticity polymer refers to a polymer that exhibits an elasticdeformation of at least 2% when measured under uniaxial tension. In thefield of materials science and engineering, the “elastic deformation” isdefined as a deformation of a material (when being mechanicallystressed) that is essentially fully recoverable and the recovery isessentially instantaneous upon release of the load. The elasticdeformation is preferably greater than 5%, more preferably greater than10%, further more preferably greater than 50%, and still more preferablygreater than 100%. The preferred types of high-capacity polymers will bediscussed later.

The application of the presently invented high-elasticity polymerencapsulation approach is not limited to any particular class of cathodeactive materials. The cathode active material layer may contain acathode active material selected from an inorganic material, an organicmaterial, a polymeric material, or a combination thereof. The inorganicmaterial may be selected from a metal oxide, metal phosphate, metalsilicide, metal selenide, transition metal sulfide, or a combinationthereof.

The inorganic material may be selected from a lithium cobalt oxide,lithium nickel oxide, lithium manganese oxide, lithium vanadium oxide,lithium-mixed metal oxide, lithium iron phosphate, lithium manganesephosphate, lithium vanadium phosphate, lithium mixed metal phosphate,lithium metal silicide, or a combination thereof.

In certain preferred embodiments, the inorganic material is selectedfrom a metal fluoride or metal chloride including the group consistingof CoF₃, MnF₃, FeF₃, VF₃, VOF₃, TiF₃, BiF₃, NiF₂, FeF₂, CuF₂, CuF, SnF₂,AgF, CuCl₂, FeCl₃, MnCl₂, and combinations thereof. In certain preferredembodiments, the inorganic material is selected from a lithiumtransition metal silicate, denoted as Li₂MSiO₄ or Li₂Ma_(x)Mb_(y)SiO₄,wherein M and Ma are selected from Fe, Mn, Co, Ni, V, or VO; Mb isselected from Fe, Mn, Co, Ni, V, Ti, Al, B, Sn, or Bi; and x+y<1.

In certain preferred embodiments, the inorganic material is selectedfrom a transition metal dichalcogenide, a transition metaltrichalcogenide, or a combination thereof. The inorganic material isselected from TiS₂, TaS₂, MoS₂, NbSe₃, MnO₂, CoO₂, an iron oxide, avanadium oxide, or a combination thereof.

The cathode active material layer may contain a metal oxide containingvanadium oxide selected from the group consisting of VO₂, Li_(x)VO₂,V₂O₅, Li_(x)V₂O₅, V₃O₈, Li_(x)V₃O₈, Li_(x)V₃O₇, V₄O₉, Li_(x)V₄O₉, V₆O₁₃,Li_(x)V₆O₁₃, their doped versions, their derivatives, and combinationsthereof, wherein 0.1<x<5.

The cathode active material layer may contain a metal oxide or metalphosphate, selected from a layered compound LiMO₂, spinel compoundLiM₂O₄, olivine compound LiMPO₄, silicate compound Li₂MSiO₄, Tavoritecompound LiMPO₄F, borate compound LiMBO₃, or a combination thereof,wherein M is a transition metal or a mixture of multiple transitionmetals.

In some embodiments, the inorganic material is selected from: (a)bismuth selenide or bismuth telluride, (b) transition metaldichalcogenide or trichalcogenide, (c) sulfide, selenide, or tellurideof niobium, zirconium, molybdenum, hafnium, tantalum, tungsten,titanium, cobalt, manganese, iron, nickel, or a transition metal; (d)boron nitride, or (e) a combination thereof.

The cathode active material layer may contain an organic material orpolymeric material selected from Poly(anthraquinonyl sulfide) (PAQS), alithium oxocarbon, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),poly(anthraquinonyl sulfide), pyrene-4,5,9,10-tetraone (PYT),polymer-bound PYT, Quino(triazene), redox-active organic material,Tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE),2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), poly(5-amino-1,4-dyhydroxyanthraquinone) (PADAQ), phosphazene disulfide polymer ([(NPS₂)₃]n),lithiated 1,4,5,8-naphthalenetetraol formaldehyde polymer,Hexaazatrinaphtylene (HATN), Hexaazatriphenylene hexacarbonitrile(HAT(CN)₆), 5-Benzylidene hydantoin, Isatine lithium salt, Pyromelliticdiimide lithium salt, tetrahydroxy-p-benzoquinone derivatives (THQLi₄),N,N′-diphenyl-2,3,5,6-tetraketopiperazine (PHP),N,N′-diallyl-2,3,5,6-tetraketopiperazine (AP),N,N′-dipropyl-2,3,5,6-tetraketopiperazine (PRP), a thioether polymer, aquinone compound, 1,4-benzoquinone, 5,7,12,14-pentacenetetrone (PT),5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ),5-amino-1,4-dyhydroxy anthraquinone (ADAQ), calixquinone, Li₄C₆O₆,Li₂C₆O₆, Li₆C₆O₆, or a combination thereof.

The thioether polymer is selected fromPoly[methanetetryl-tetra(thiomethylene)] (PMTTM),Poly(2,4-dithiopentanylene) (PDTP), a polymer containingPoly(ethene-1,1,2,2-tetrathiol) (PETT) as a main-chain thioetherpolymers, a side-chain thioether polymer having a main-chain consistingof conjugating aromatic moieties, and having a thioether side chain as apendant, Poly(2-phenyl-1,3-dithiolane) (PPDT),Poly(l,4-di(1,3-dithiolan-2-yl)benzene) (PDDTB),poly(tetrahydrobenzodithiophene) (PTHBDT),poly[1,2,4,5-tetrakis(propylthio)benzene] (PTKPTB, orpoly[3,4(ethylenedithio)thiophene] (PEDTT).

In other embodiments, the cathode active material layer contains anorganic material selected from a phthalocyanine compound, such as copperphthalocyanine, zinc phthalocyanine, tin phthalocyanine, ironphthalocyanine, lead phthalocyanine, nickel phthalocyanine, vanadylphthalocyanine, fluorochromium phthalocyanine, magnesium phthalocyanine,manganous phthalocyanine, dilithium phthalocyanine, aluminumphthalocyanine chloride, cadmium phthalocyanine, chlorogalliumphthalocyanine, cobalt phthalocyanine, silver phthalocyanine, ametal-free phthalocyanine, a chemical derivative thereof, or acombination thereof.

The particles of the anode active material may be in the form of a nanoparticle, nano wire, nano fiber, nano tube, nano sheet, nano platelet,nano disc, nano belt, nano ribbon, or nano horn. They can benon-lithiated (when incorporated into the anode active material layer)or pre-lithiated to a desired extent (up to the maximum capacity asallowed for a specific element or compound.

Preferably and typically, the high-elasticity polymer has a lithium ionconductivity no less than 10⁻⁵ S/cm, more preferably no less than 10⁻⁴S/cm, further preferably no less than 10⁻³ S/cm, and most preferably noless than 10⁻² S/cm. In some embodiments, the high-elasticity polymer isa neat polymer having no additive or filler dispersed therein. Inothers, the high-elasticity polymer is a polymer matrix compositecontaining from 0.1% to 50% (preferably 1% to 35%) by weight of alithium ion-conducting additive dispersed in an UHMW polymer matrixmaterial. The high-elasticity polymer must have a high elasticity(elastic deformation strain value >2%). An elastic deformation is adeformation that is fully recoverable and the recovery process isessentially instantaneous (no significant time delay). Thehigh-elasticity polymer can exhibit an elastic deformation from 5% up to300% (3 times of its original length), more typically from 10% to 200%,and further more typically from 30% to 100%. It may be noted thatalthough a metal typically has a high ductility (i.e. can be extended toa large extent without breakage), the majority of the deformation isplastic deformation (non-recoverable) and only a small amount of elasticdeformation (typically <1% and more typically <0.2%).

In some preferred embodiments, the high-elasticity polymer contains aselect group of ultra-high molecular weight polymers that exhibit aunique combination of a high elasticity (high elastic deformationstrain) and high lithium-ion conductivity. These UHMW polymers cancontain a lithium salt to further increase the lithium ion conductivity.An UHMW polymer may also contain an electron-conducting materialdispersed therein. Thus, the high-elasticity is preferably lithiumion-conducting and electron-conducting.

In certain preferred embodiments, the high-elasticity polymer containsan ultrahigh molecular weight (UHMW) polymer preferably selected fromUHMW polyacrylonitrile (UHMW PAN), polyethylene oxide (UHMW PEO),polypropylene oxide (UHMW PPO), polyethylene glycol (UHMW PEG),polyvinyl alcohol (UHMW PVA), polyacrylamide (UHMW PAA), poly(methylmethacrylate) (UHMW PMMA), poly(methyl ether acrylate) (UHMW PMEA), acopolymer thereof, a sulfonated derivative thereof, a chemicalderivative thereof, or a combination thereof.

The first step for producing encapsulated active material particles isto dissolve a UHMW polymer in a solvent to form a solution.Subsequently, particles of a cathode active material (e.g. lithium metaloxide, lithium metal fluoride, etc.) can be dispersed in apolymer-solvent solution to form a suspension (also referred to asdispersion or slurry) of an active material particle-polymer mixture.This suspension can then be subjected to a solvent removal treatmentwhile individual particles remain substantially separated from oneanother. The polymer precipitates out to deposit on surfaces of theseactive material particles. This can be accomplished, for instance, viaspray drying, ultrasonic spraying, air-assisted spraying,aerosolization, and other secondary particle formation procedures. Thesetechniques will be discussed later.

One may also choose to add some lithium salt into the slurry. Forinstance, the procedure may begin with dissolving UHMW PVA in a liquidsolvent to form a solution. A lithium salt, LiPF₆, can then be addedinto the solution at a desired weight percentage. Then, particles of aselected cathode active material are introduced into the mixturesolution to form a slurry. The slurry may then be subjected to amicro-encapsulation procedure to produce cathode active materialparticles coated with an embracing layer of UHMW PVA containing LiPF₆dispersed therein (in the amorphous zones of the polymer).

The aforementioned high-elasticity polymers may be used alone toencapsulate the cathode active material particles. Alternatively, theUHMW polymer can be mixed with a broad array of elastomers, electricallyconducting polymers, lithium ion-conducting materials, and/orstrengthening materials (e.g. carbon nanotube, carbon nano-fiber, orgraphene sheets).

A broad array of elastomers can be mixed with an UHMW polymer to form ablend, co-polymer, or interpenetrating network that encapsulates thecathode active material particles. The elastomeric material may beselected from natural polyisoprene (e.g. cis-1,4-polyisoprene naturalrubber (NR) and trans-1,4-polyisoprene gutta-percha), syntheticpolyisoprene (IR for isoprene rubber), polybutadiene (BR for butadienerubber), chloroprene rubber (CR), polychloroprene (e.g. Neoprene,Baypren etc.), butyl rubber (copolymer of isobutylene and isoprene,IIR), including halogenated butyl rubbers (chloro butyl rubber (CIIR)and bromo butyl rubber (BIIR), styrene-butadiene rubber (copolymer ofstyrene and butadiene, SBR), nitrile rubber (copolymer of butadiene andacrylonitrile, NBR), EPM (ethylene propylene rubber, a copolymer ofethylene and propylene), EPDM rubber (ethylene propylene diene rubber, aterpolymer of ethylene, propylene and a diene-component),epichlorohydrin rubber (ECO), polyacrylic rubber (ACM, ABR), siliconerubber (SI, Q, VMQ), fluorosilicone rubber (FVMQ), fluoroelastomers(FKM, and FEPM; such as Viton, Tecnoflon, Fluorel, Aflas and Dai-E1),perfluoroelastomers (FFKM: Tecnoflon PFR, Kalrez, Chemraz, Perlast),polyether block amides (PEBA), chlorosulfonated polyethylene (CSM; e.g.Hypalon), and ethylene-vinyl acetate (EVA), thermoplastic elastomers(TPE), protein resilin, protein elastin, ethylene oxide-epichlorohydrincopolymer, polyurethane, urethane-urea copolymer, and combinationsthereof.

In some embodiments, an UHMW polymer can form a polymer matrix compositecontaining a lithium ion-conducting additive dispersed in thehigh-elasticity polymer matrix material, wherein the lithiumion-conducting additive is selected from Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH,LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y),or a combination thereof, wherein X=F, Cl, I, or Br, R=a hydrocarbongroup, x=0-1, y=1-4.

In some embodiments, the UHMW polymer can be mixed with a lithiumion-conducting additive, which contains a lithium salt selected fromlithium perchlorate, LiClO₄, lithium hexafluorophosphate, LiPF₆, lithiumborofluoride, LiBF₄, lithium hexafluoroarsenide, LiAsF₆, lithiumtrifluoro-metasulfonate, LiCF₃ SO₃, bis-trifluoromethyl sulfonylimidelithium, LiN(CF₃SO₂)₂, lithium bis(oxalato)borate, LiBOB, lithiumoxalyldifluoroborate, LiBF₂C₂O₄, lithium oxalyldifluoroborate,LiBF₂C₂O₄, lithium nitrate, LiNO₃, Li-Fluoroalkyl-Phosphates,LiPF₃(CF₂CF₃)₃, lithium bisperfluoro-ethysulfonylimide, LiBETI, lithiumbis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide,lithium trifluoromethanesulfonimide, LiTFSI, an ionic liquid-basedlithium salt, or a combination thereof.

The UHMW polymer may form a mixture, blend, or semi-interpenetratingnetwork with an electron-conducting polymer selected from polyaniline,polypyrrole, polythiophene, polyfuran, a bi-cyclic polymer, derivativesthereof (e.g. sulfonated versions), or a combination thereof. In someembodiments, the UHMW polymer may form a mixture, co-polymer, orsemi-interpenetrating network with a lithium ion-conducting polymerselected from poly(ethylene oxide) (PEO), Polypropylene oxide (PPO),poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA),poly(vinylidene fluoride) (PVdF), Poly bis-methoxyethoxyethoxide-phosphazenex, Polyvinyl chloride, Polydimethylsiloxane,poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a derivativethereof (e.g. sulfonated versions), or a combination thereof.

Unsaturated rubbers that can be mixed with the UHMW polymer includenatural polyisoprene (e.g. cis-1,4-polyisoprene natural rubber (NR) andtrans-1,4-polyisoprene gutta-percha), synthetic polyisoprene (IR forisoprene rubber), polybutadiene (BR for butadiene rubber), chloroprenerubber (CR), polychloroprene (e.g. Neoprene, Baypren etc.), butyl rubber(copolymer of isobutylene and isoprene, IIR), including halogenatedbutyl rubbers (chloro butyl rubber (CIIR) and bromo butyl rubber (BIIR),styrene-butadiene rubber (copolymer of styrene and butadiene, SBR),nitrile rubber (copolymer of butadiene and acrylonitrile, NBR),

Saturated rubbers and related elastomers in this category include EPM(ethylene propylene rubber, a copolymer of ethylene and propylene), EPDMrubber (ethylene propylene diene rubber, a terpolymer of ethylene,propylene and a diene-component), epichlorohydrin rubber (ECO),polyacrylic rubber (ACM, ABR), silicone rubber (SI, Q, VMQ),fluorosilicone rubber (FVMQ), fluoroelastomers (FKM, and FEPM; such asViton, Tecnoflon, Fluorel, Aflas and Dai-E1), perfluoroelastomers (FFKM:Tecnoflon PFR, Kalrez, Chemraz, Perlast), polyether block amides (PEBA),chlorosulfonated polyethylene (CSM; e.g. Hypalon), and ethylene-vinylacetate (EVA), thermoplastic elastomers (TPE), protein resilin, andprotein elastin. Polyurethane and its copolymers (e.g. urea-urethanecopolymer) are particularly useful elastomeric shell materials forencapsulating active material particles.

Several micro-encapsulation processes may be used to encapsulateparticles of an active material. These processes typically require thehigh-elasticity polymer or its precursor (monomer or oligomer) to bedissolvable in a solvent. Fortunately, all the UHMW polymers or theirprecursors used herein are soluble in some common solvents. The polymeror its precursor can be readily dissolved in a common organic solvent toform a solution. This solution can then be used to encapsulate solidparticles via several of the micro-encapsulation methods to be discussedin what follows. Upon encapsulation, the polymer shell is thenpolymerized.

There are three broad categories of micro-encapsulation methods that canbe implemented to produce high-elasticity polymer-encapsulated particlesof an active material: physical methods, physico-chemical methods, andchemical methods. The physical methods include pan-coating,air-suspension coating, centrifugal extrusion, vibration nozzle, andspray-drying methods. The physico-chemical methods include ionotropicgelation and coacervation-phase separation methods. The chemical methodsinclude interfacial polycondensation, interfacial cross-linking, in-situpolymerization, and matrix polymerization.

Pan-coating method: The pan coating process involves tumbling the activematerial particles in a pan or a similar device while the encapsulatingmaterial (e.g. monomer/oligomer, polymer melt, polymer/solvent solution)is applied slowly until a desired encapsulating shell thickness isattained.

Air-suspension coating method: In the air suspension coating process,the solid particles (core material) are dispersed into the supportingair stream in an encapsulating chamber. A controlled stream of apolymer-solvent solution (polymer or its monomer or oligomer dissolvedin a solvent; or its monomer or oligomer alone in a liquid state) isconcurrently introduced into this chamber, allowing the solution to hitand coat the suspended particles. These suspended particles areencapsulated (fully coated) with a polymer or its precursor moleculeswhile the volatile solvent is removed, leaving a very thin layer ofpolymer (or its precursor, which is cured/hardened subsequently) onsurfaces of these particles. This process may be repeated several timesuntil the required parameters, such as full-coating thickness (i.e.encapsulating shell or wall thickness), are achieved. The air streamwhich supports the particles also helps to dry them, and the rate ofdrying is directly proportional to the temperature of the air stream,which can be adjusted for optimized shell thickness.

In a preferred mode, the particles in the encapsulating zone portion maybe subjected to re-circulation for repeated coating. Preferably, theencapsulating chamber is arranged such that the particles pass upwardsthrough the encapsulating zone, then are dispersed into slower movingair and sink back to the base of the encapsulating chamber, enablingrepeated passes of the particles through the encapsulating zone untilthe desired encapsulating shell thickness is achieved.

Centrifugal extrusion: Particles of an active material may beencapsulated using a rotating extrusion head containing concentricnozzles. In this process, a stream of core fluid (slurry containingparticles of an active material dispersed in a solvent) is surrounded bya sheath of shell solution or melt. As the device rotates and the streammoves through the air it breaks, due to Rayleigh instability, intodroplets of core, each coated with the shell solution. While thedroplets are in flight, the molten shell may be hardened or the solventmay be evaporated from the shell solution. If needed, the capsules canbe hardened after formation by catching them in a hardening bath. Sincethe drops are formed by the breakup of a liquid stream, the process isonly suitable for liquid or slurry. A high production rate can beachieved. Up to 22.5 kg of microcapsules can be produced per nozzle perhour and extrusion heads containing 16 nozzles are readily available.

Vibrational nozzle method: Core-shell encapsulation ormatrix-encapsulation of an active material can be conducted using alaminar flow through a nozzle and vibration of the nozzle or the liquid.The vibration has to be done in resonance with the Rayleigh instability,leading to very uniform droplets. The liquid can consist of any liquidswith limited viscosities (1-50,000 mPa·s): emulsions, suspensions orslurry containing the active material. The solidification can be doneaccording to the used gelation system with an internal gelation (e.g.sol-gel processing, melt) or an external (additional binder system, e.g.in a slurry).

Spray-drying: Spray drying may be used to encapsulate particles of anactive material when the active material is dissolved or suspended in amelt or polymer solution. In spray drying, the liquid feed (solution orsuspension) is atomized to form droplets which, upon contacts with hotgas, allow solvent to get vaporized and thin polymer shell to fullyembrace the solid particles of the active material.

Coacervation-phase separation: This process consists of three stepscarried out under continuous agitation:

-   (a) Formation of three immiscible chemical phases: liquid    manufacturing vehicle phase, core material phase and encapsulation    material phase. The core material is dispersed in a solution of the    encapsulating polymer (or its monomer or oligomer). The    encapsulating material phase, which is an immiscible polymer in    liquid state, is formed by (i) changing temperature in polymer    solution, (ii) addition of salt, (iii) addition of non-solvent,    or (iv) addition of an incompatible polymer in the polymer solution.-   (b) Deposition of encapsulation shell material: core material being    dispersed in the encapsulating polymer solution, encapsulating    polymer material coated around core particles, and deposition of    liquid polymer embracing around core particles by polymer adsorbed    at the interface formed between core material and vehicle phase; and-   (c) Hardening of encapsulating shell material: shell material being    immiscible in vehicle phase and made rigid via thermal,    cross-linking, or dissolution techniques.

Interfacial polycondensation and interfacial cross-linking: Interfacialpolycondensation entails introducing the two reactants to meet at theinterface where they react with each other. This is based on the conceptof the Schotten-Baumann reaction between an acid chloride and a compoundcontaining an active hydrogen atom (such as an amine or alcohol),polyester, polyurea, polyurethane, or urea-urethane condensation. Underproper conditions, thin flexible encapsulating shell (wall) formsrapidly at the interface. A solution of the active material and a diacidchloride are emulsified in water and an aqueous solution containing anamine and a polyfunctional isocyanate is added. A base may be added toneutralize the acid formed during the reaction. Condensed polymer shellsform instantaneously at the interface of the emulsion droplets.Interfacial cross-linking is derived from interfacial polycondensation,wherein cross-linking occurs between growing polymer chains and amulti-functional chemical groups to form a polymer shell material.

In-situ polymerization: In some micro-encapsulation processes, activematerials particles are fully coated with a monomer or oligomer first.Then, direct polymerization and cross-linking of the monomer or oligomeris carried out on the surfaces of these material particles.

Matrix polymerization: This method involves dispersing and embedding acore material in a polymeric matrix during formation of the particles.This can be accomplished via spray-drying, in which the particles areformed by evaporation of the solvent from the matrix material. Anotherpossible route is the notion that the solidification of the matrix iscaused by a chemical change.

In the following examples, UHMW PEO, UHMW PPO, and UHMW PAN were used asthree examples of UHMW polymers to illustrate the best mode of practice.Other UHMW polymers can be similarly used. These should not be construedas limiting the scope of invention.

EXAMPLE 1 Cathode Active Material Layers Containing High-Elasticity UHMWPolymer-encapsulated V₂O₅ Particles

Cathode active material layers were prepared from V₂O₅ particles andgraphene-embraced V₂O₅ particles, respectively. V₂O₅ particles werecommercially available. Graphene-embraced V₂O₅ particles were preparedin-house. In a typical experiment, vanadium pentoxide gels were obtainedby mixing V₂O₅ in a LiCl aqueous solution. The Li⁺ exchanged gelsobtained by interaction with LiCl solution (the Li:V molar ratio waskept as 1:1) was mixed with a GO suspension and then placed in aTeflon-lined stainless steel 35 ml autoclave, sealed, and heated up to180° C. for 12 h. After such a hydrothermal treatment, the green solidswere collected, thoroughly washed, ultrasonicated for 2 minutes, anddried at 70° C. for 12 h followed by mixing with another 0.1% GO inwater, ultrasonicating to break down nano-belt sizes, and thenspray-drying at 200° C. to obtain graphene-embraced V₂O₅ compositeparticulates.

Selected amounts of V₂O₅ particles and graphene-embraced V₂O₅ particles,respectively, were then each made into UHMW PEO-based high-elasticitypolymer-encapsulated particulates according to the following procedure:

UHMW PEO was dissolved in DI-water (1.6 wt. %) to form a homogenous andclear solution first. Then, two routes were followed to preparepolymer-encapsulated V₂O₅ particles and graphene-embraced V₂O₅particles. In the first route, V₂O₅ particles and graphene-embraced V₂O₅particles, respectively, were dispersed in the UHMW PEO-water solutionto form a slurry. In some samples, 0.5%-5% of a conductive filler (e.g.graphene sheets) was added into the slurry. The slurries were separatelyspray-dried to form particulates of polymer-encapsulated V₂O₅ andgraphene-embraced V₂O₅ particles.

In the second route, 1-45% of lithium salt (LiClO₄) was dissolved in thesolution to form a series of lithium-salt containing solutions. Then,V₂O₅ particles or graphene-embraced V₂O₅ particles were dispersed in thelithium-containing UHMW PEO-water solution to form a series of slurries.In some samples, 0.5%-5% of a conductive filler (e.g. graphene sheets)was added into the slurry. Each slurry was spray-dried to formparticulates of polymer- or polymer/lithium salt-encapsulated V₂O₅ orgraphene-embraced V₂O₅ particles. The polymer or polymer/lithium saltshell can contain some conducting material (graphene sheets, in thiscase).

Some of the particulate samples were subsequently soaked in a solvent(preferably a desired lithium-ion battery electrolyte solvent such asethylene carbonate, EC), allowing the solvent to permeate into theamorphous zones of the polymer phase embracing the anode particles. TheUHMW polymer shell thickness was varied from 356 nm to 1.66 μm.

UHMW PEO-water solution was also cast onto glass surface and dried toform PEO films. Upon thorough drying, the polymer films were soaked in adesired solvent (e.g. EC) to form a rubber-like polymer. Several tensiletesting specimens were cut from each polymer film containing a solvent(e.g. EC) and tested with a universal testing machine. Therepresentative tensile stress-strain curves of polymers are shown inFIG. 3(A), which indicate that this polymer has an elastic deformationof approximately 150%. This value is for a neat polymer (containing somesolvent) without any solid additive (no lithium salt and no conductiveadditive). The addition of up to 30% by weight of a lithium salttypically reduces this elasticity down to a reversible tensile strainfrom 5% to 60%.

For electrochemical testing, a comparative electrode using aconventional cathode (no encapsulation) was also prepared. The workingelectrodes were prepared by mixing 85 wt. % V₂O₅ or 88% ofgraphene-embraced V₂O₅ particles, 5-8 wt. % CNTs, and 7 wt. %polyvinylidene fluoride (PVDF) binder dissolved inN-methyl-2-pyrrolidinoe (NMP) to form a slurry of 5 wt. % total solidcontent. After coating the slurries on Al foil, the electrodes weredried at 120° C. in vacuum for 2 h to remove the solvent beforepressing. Then, the electrodes were cut into a disk (φ=12 mm) and driedat 100° C. for 24 h in vacuum.

Electrochemical measurements were carried out using CR2032 (3V)coin-type cells with lithium metal as the counter/reference electrode,Celgard 2400 membrane as separator, and 1 M LiPF₆ electrolyte solutiondissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate(DEC) (EC-DEC, 1:1 v/v). The cell assembly was performed in anargon-filled glove-box. The CV measurements were carried out using aCH-6 electrochemical workstation at a scanning rate of 1 mV/s. Theelectrochemical performance of the cell featuring high-elasticitypolymer binder and that containing PVDF binder were evaluated bygalvanostatic charge/discharge cycling at a current density of 50 mA/gusing an Arbin electrochemical workstation.

Summarized in FIG. 3(B) are the specific intercalation capacity curvesof four lithium cells: cathode containing un-encapsulated V₂O₅particles, cathode containing un-encapsulated but graphene-embraced V₂O₅particles, cathode containing UHMW PEO polymer-encapsulated V₂O₅particles, and cathode containing UHMW PEO polymer-encapsulatedgraphene-embraced V₂O₅ particles. As the number of cycles increases, thespecific capacity of the un-encapsulated V₂O₅ electrode drops at thefastest rate. In contrast, the presently invented UHMW PEO polymerencapsulation provides the battery cell with a significantly more stableand high specific capacity for a large number of cycles. These data haveclearly demonstrated the surprising and superior performance of thepresently invented UHMW polymer encapsulation approach.

The high-elasticity UHMW polymer encapsulation shell appears to becapable of reversibly deforming to a great extent without breakage whenthe active material particles expand and shrink. The polymer alsoremains chemically bonded to the binder resin when the encapsulatedparticles expand or shrink. In contrast, the PVDF binder is broken ordetached from some of the non-encapsulated active material particles.These were observed by using SEM to examine the surfaces of theelectrodes recovered from the battery cells after some numbers ofcharge-discharge cycles.

EXAMPLE 2 High-elasticity Polymer Binder-bonded Lithium Iron Phosphate(LFP) Particles

The high-elasticity polymer for encapsulation of LFP particles was basedon ultra-high molecular weight polyacrylonitrile (UHMW PAN). UHMW PAN(0.3 g) was dissolved in 5 ml of dimethylformamide (DMF) to form asolution. The LFP particles were then dispersed in the solution to forma slurry. The slurries were then separately subjected to amicro-encapsulation procedure to produce anode active material particleshaving entire exterior surfaces being coated with an embracing layer ofthe polymers.

Polymer films for elasticity testing were cast from the preparedsolutions on a glass support, followed by solvent evaporation at 70° C.under a fume hood. To remove the traces of DMF, the films werethoroughly dried in a vacuum (<1 Torr) at 70° C. for 48 h. The polymerfilms were soaked in propylene carbonate (PC) to form PC-plasticizedUHMW PAN films. Tensile testing was also conducted on these films andsome testing results are summarized in FIG. 4(A). This series ofpolymers can be elastically stretched up to approximately 80%.

The battery cells from the high-elasticity polymer-encapsulatedcarbon-coated LFP particles and non-encapsulated carbon-coated LFPparticles were prepared using a procedure similar to that described inExample 1. FIG. 4(B) shows that the cathode prepared according to thepresently invented high-elasticity polymer encapsulation approach offersa significantly more stable cycling behavior and higher reversiblecapacity compared to the non-encapsulated LFP particle-based cathode.The high-elasticity polymer is more capable of holding the activematerial particles and conductive additive together, significantlyimproving the structural integrity of the active material electrode. Thehigh-elasticity polymer also acts to isolate the electrolyte from theactive material yet still allowing for easy diffusion of lithium ions.

EXAMPLE 3 Metal Fluoride Nano Particles Encapsulated by an UHMW PPO

For encapsulation of FeF₃ nano particles, an UHMW PPO polymer wasimplemented as an embracing polymer shell by using a procedure similarto that described in Example 1. Commercially available powders of CoF₃,MnF₃, FeF₃, VF₃, VOF₃, TiF₃, and BiF₃ were subjected to high-intensityball-milling to reduce the particle size down to approximately 0.5-2.3μm. Each type of these metal fluoride particles, along with graphenesheets (as a conductive additive), was then added into a UHMWPPO-solvent liquid suspension to form a multiple-component slurry. Theslurry was then spray-dried to form isolated polymer embraced particles.

Shown in FIG. 5 are the discharge capacity curves of two coin cellshaving two different types of cathode active materials: (1)high-elasticity UHMW PPO polymer-encapsulated metal fluoride particlesand (2) non-encapsulated metal fluorides. These results have clearlydemonstrated that the high-elasticity UHMW polymer encapsulationstrategy provides excellent protection against capacity decay of alithium metal battery featuring a high-capacity cathode active material.

The high-elasticity polymer appears to be capable of reversiblydeforming without breakage when the cathode active material particlesexpand and shrink. The polymer also remains chemically bonded to thebinder resin when the active particles expand or shrink. In contrast,both SBR and PVDF, the two conventional binder resins, are broken ordetached from some of the non-encapsulated active material particles.The high-elasticity polymer has contributed to the structural stabilityof the electrode layer. These were observed by using SEM to examine thesurfaces of the electrodes recovered from the battery cells after somenumbers of charge-discharge cycles.

EXAMPLE 4 Metal Naphthalocyanine/Reduced Graphene Oxide (FePc/RGO)Hybrid Particulates Encapsulated by a High-elasticity Polymer

Particles of combined FePc/graphene sheets were obtained by ball-millinga mixture of FePc and RGO in a milling chamber for 30 minutes. Theresulting FePc/RGO mixture particles were potato-like in shape. Some ofthese mixture particles were encapsulated by a high-elasticity UHMW PANpolymer using the pan-coating procedure. Two lithium cells wereprepared, each containing a Li foil anode, a porous separator, and acathode layer of FePc/RGO particles (encapsulated or un-encapsulated).

The cycling behaviors of these 2 lithium cells are shown in FIG. 6,which indicates that the lithium-organic cell having a high-elasticitypolymer-encapsulated particulates in the cathode layer exhibits asignificantly more stable cycling response. This encapsulation polymerreduces or eliminates direct contact between the catalytic transitionmetal element (Fe) and the electrolyte, yet still being permeable tolithium ions. This polymer also completely eliminates the dissolution ofnaphthalocyanine compounds in the liquid electrolyte. This approach hassignificantly increased the cycle life of all lithium-organic batteries.

EXAMPLE 5 Effect of Lithium Ion-conducting Additive in a High-elasticityPolymer

A wide variety of lithium ion-conducting additives were added to severaldifferent polymer matrix materials to prepare encapsulation shellmaterials for protecting core particles of an anode active material. Thelithium ion conductivity vales of the resulting polymer/salt complexmaterials are summarized in Table 1 below. We have discovered that thesepolymer composite materials are suitable encapsulation shell materialsprovided that their lithium ion conductivity at room temperature is noless than 10⁻⁶ S/cm. With these materials, lithium ions appear to becapable of readily diffusing in and out of the encapsulation shellhaving a thickness no greater than 1 μm. For thicker shells (e.g. 10μm), a lithium ion conductivity at room temperature no less than 10⁻⁴S/cm would be required.

TABLE 1 Lithium ion conductivity of various UHMW polymer compositions asa shell material for protecting anode active material particles. SampleLithium-conducting UHMW polymer + PC or No. additive EC (1-2 μm thick)Li-ion conductivity (S/cm) UE-1p Li₂CO₃ + (CH₂OCO₂Li)₂ 70-99% PEO 2.2 ×10⁻⁴ to 3.3 × 10⁻³ S/cm UE-2p Li₂CO₃ + (CH₂OCO₂Li)₂ 65-99% PAN 4.7 ×10⁻⁴ to 2.1 × 10⁻³ S/cm UE-3p Li₂CO₃ + (CH₂OCO₂Li)₂ 65-99% PEO + PPO 8.4× 10⁻⁴ to 3.8 × 10⁻³ S/cm UD-4p Li₂CO₃ + (CH₂OCO₂Li)₂ 70-99% PMMA 7.8 ×10⁻⁵ to 2.3 × 10⁻⁴ S/cm UD-5p Li₂CO₃ + (CH₂OCO₂Li)₂ 75-99% PVA 6.9 ×10⁻⁵ to 1.2 × 10⁻³ S/cm UB1p LiF + LiOH + Li₂C₂O₄ 60-90% PVA 8.7 × 10⁻⁵to 2.3 × 10⁻³ S/cm UB2p LiF + HCOLi 80-99% PVA 3.8 × 10⁻⁵ to 4.6 × 10⁻⁴S/cm UB3p LiOH 70-99% PPO 3.5 × 10⁻³ to 1.2 × 10⁻² S/cm UB4p Li₂CO₃70-99% PPO 2.2 × 10⁻³ to 9.5 × 10⁻³ S/cm UB5p Li₂C₂O₄ 70-99% PPO 1.4 ×10⁻³ to 1.2 × 10⁻² S/cm UB6p Li₂CO₃ + LiOH 70-99% PEG 1.5 × 10⁻³ to 1.6× 10⁻² S/cm UC1p LiClO₄ 70-99% PEO 4.6 × 10⁻⁴ to 2.2 × 10⁻³ S/cm UC2pLiPF₆ 70-99% PEO 3.4 × 10⁻⁴ to 7.5 × 10⁻³ S/cm UC3p LiBF₄ 70-99% PAA 1.1× 10⁻⁴ to 1.6 × 10⁻³ S/cm UC4p LiBOB + LiNO₃ 70-99% PMEA 2.2 × 10⁻⁴ to4.3 × 10⁻³ S/cm US1p Sulfonated polyaniline 85-99% PAN 5.8 × 10⁻⁵ to 9.2× 10⁻⁴ S/cm US2p Sulfonated SBR 85-99% PEO 1.6 × 10⁻⁴ to 1.2 × 10⁻³ S/cmUS3p Sulfonated PVDF 80-99% PEG 3.2 × 10⁻⁴ to 2.3 × 10⁻⁴ S/cm

EXAMPLE 6 Cycle Stability of Various Rechargeable Lithium Battery Cells

In lithium-ion battery industry, it is a common practice to define thecycle life of a battery as the number of charge-discharge cycles thatthe battery suffers 20% decay in capacity based on the initial capacitymeasured after the required electrochemical formation. Summarized inTable 2 below are the cycle life data of a broad array of batteriesfeaturing presently invented electrodes containing anode active materialparticles bonded by different binder materials. Table 2: Cycle life dataof various lithium secondary (rechargeable batteries.

TABLE 2 Cycle life data of various lithium secondary (rechargeable)batteries. Initial Cycle life Encapsulation Type & % of cathode activecapacity (No. of Sample ID polymer material (mAh/g) cycles) CuCl₂-1eUHMW PEO 85% by wt. CuCl₂ particles (80 530 1677 nm) + 7% graphite + 8%binder CuCl₂-2e none 85% by wt. CuCl₂ particles (80 527 113 nm) + 7%graphite + 8% binder BiF₃-1e none 85% by wt. BiFe₃ particles + 7% 275115 graphene + 8% binder BiF₃-2e UHMW PAN 85% by wt. BiFe₃ particles +7% 276 1,334 graphene + 8% binder Li₂MnSiO₄-1e UHMW PPO 85% C-coatedLi₂MnSiO₄ + 7% 252 2,525 CNT + 8% binder Li₂MnSiO₄-2e none 85% C-coatedLi₂MnSiO₄ + 7% 252 543 CNT + 8% binder Li₆C₆O₆-1e UHMW PEO +Li₆C₆O₆-graphene ball-milled 440 1,465 20% polyaniline Li₆C₆O₆-2e noneLi₆C₆O₆-graphene ball-milled 438 116 MoS₂-1e UHMW PEO + 85% MoS₂ + 8%graphite 225 2,444 1% graphene platelets + binder MoS₂-2e none 85%MoS₂ + 8% graphite 225 156 platelets + binder

These data further confirm that the high-elasticity UHMW polymerencapsulation strategy is surprisingly effective in alleviating thecathode structural instability-induced capacity decay problems. Thehigh-elasticity UHMW polymer encapsulation layer appears to be capableof preventing liquid electrolyte from being in direct physical contactwith the cathode active material and, thus, preventing the catalyticelements (e.g. Fe, Mn, Ni, Co, etc.) in the cathode active material fromcatalyzing the decomposition of the electrolyte to form volatile orflammable gas molecules inside the battery cell. This otherwise couldcause fast capacity decay and fire and explosion hazard. Thehigh-elasticity UHMW polymer encapsulation layer also preventsdissolution of an organic or polymeric active material in the liquidelectrolyte, which otherwise would lead to loss of the active materialand, thus, capacity loss.

We claim:
 1. A particulate of a positive electrode active material for alithium battery, said particulate comprising one or a plurality ofpositive electrode active material particles being embraced orencapsulated by a thin layer of a polymer having a recoverable tensilestrain no less than 5%, a lithium ion conductivity no less than 10⁻⁶S/cm at room temperature, and a thickness of the thin layer is from 0.5nm to 10 μm, wherein said polymer contains an ultrahigh molecular weightpolymer having a molecular weight from 0.5×10⁶ to 9×10⁶ grams/mole andsaid ultrahigh molecular weight polymer is selected from polyethyleneoxide, polypropylene oxide, polyethylene glycol, polyvinyl alcohol,polyacrylamide, poly(methyl methacrylate), poly(methyl ether acrylate),a copolymer thereof, a sulfonated derivative thereof, a chemicalderivative thereof, and combinations thereof, and wherein said lithiumbattery is selected from a lithium-ion battery or lithium metal battery,excluding metal-air and metal-sulfur battery.
 2. The particulate ofclaim 1, wherein said ultrahigh molecular weight polymer has themolecular weight from 0.5×10⁶ to less than 5×10⁶ grams/mole.
 3. Theparticulate of claim 1, wherein said ultrahigh molecular weight polymerhas the molecular weight from 1×10⁶ to less than 3×10⁶ grams/mole. 4.The particulate of claim 1, wherein said thin layer of polymer has thethickness from 1 nm to 1 μm.
 5. The particulate of claim 1, wherein saidthin layer of polymer has the thickness less than 100 nm.
 6. Theparticulate of claim 1, wherein said thin layer of polymer has thethickness less than 10 nm.
 7. The particulate of claim 1, wherein saidpolymer has the lithium ion conductivity from 10⁻⁴ S/cm to 10⁻² S/cm. 8.The particulate of claim 1, wherein said polymer is a neat polymerhaving no additive or filler dispersed therein.
 9. The particulate ofclaim 1, wherein said ultra-high molecular weight polymer contains from0.1% to 50% by weight of a lithium ion-conducting additive dispersedtherein, or contains therein from 0.1% by weight to 10% by weight of areinforcement nano filament selected from carbon nanotube, carbonnano-fiber, graphene, or a combination thereof.
 10. The particulate ofclaim 1, wherein said ultra-high molecular weight polymer is mixed witha lithium ion-conducting additive to form a composite wherein saidlithium ion-conducting additive is dispersed in said polymer and isselected from Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi,(ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y), or a combination thereof,wherein X=F, Cl, I, or Br, R=a hydrocarbon group, 0<x≤1 and 1≤y≤4. 11.The particulate of claim 1, wherein the ultra-high molecular weightpolymer forms a mixture, blend, copolymer, or semi-interpenetratingnetwork with a lithium ion-conducting polymer selected frompoly(ethylene oxide) (PEO), polypropylene oxide (PPO),poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA),poly(vinylidene fluoride) (PVdF), poly bis-methoxyethoxyethoxide-phosphazenex, polyvinyl chloride, polydimethylsiloxane,poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a sulfonatedderivative thereof, or a combination thereof.
 12. The particulate ofclaim 1, wherein said ultrahigh molecular weight polymer contains alithium salt and/or a liquid solvent dispersed between chains of saidultrahigh molecular weight polymer.
 13. The particulate of claim 12,wherein said liquid solvent is selected from 1,3-dioxolane (DOL),1,2-dimethoxyethane (DME), tetraethylene glycol dimethylether (TEGDME),poly(ethylene glycol) dimethyl ether (PEGDME), diethylene glycol dibutylether (DEGDBE), 2-ethoxyethyl ether (EEE), sulfone, sulfolane, ethylenecarbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC),methylethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate,methyl propionate, gamma-butyrolactone (γ-BL), acetonitrile (AN), ethylacetate (EA), propyl formate (PF), methyl formate (MF), toluene, xylene,methyl acetate (MA), fluoroethylene carbonate (FEC), vinylene carbonate(VC), allyl ethyl carbonate (AEC), a hydrofluoroether, an ionic liquidsolvent, and combinations thereof.
 14. The particulate of claim 12,wherein said lithium salt is selected from lithium perchlorate (LiClO₄),lithium hexafluorophosphate (LiPF₆), lithium borofluoride (LiBF₄),lithium hexafluoroarsenide (LiAsF₆), lithium trifluoro-methanesulfonate(LiCF₃SO₃), bis-trifluoromethyl sulfonylimide lithium (LiN(CF₃SO₂)₂),lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate(LiBF₂C₂O₄), lithium nitrate (LiNO₃), Li-fluoroalkyl-phosphate, lithiumbisperfluoro-ethysulfonylimide (LiBETI), lithiumbis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide,lithium trifluoromethanesulfonimide (LiTFSI), an ionic liquid-basedlithium salt, and combinations thereof.
 15. The particulate of claim 1,wherein said ultra-high molecular weight polymer is mixed with anelectron-conducting polymer selected from polyaniline, polypyrrole,polyfuran, a bi-cyclic polymer, a sulfonated derivative thereof, or acombination thereof to form a blend, co-polymer, orsemi-interpenetrating network.
 16. The particulate of claim 1, whereinsaid thin layer contains a conductive additive selected from graphite,graphene, or carbon material, or a combination thereof.
 17. Theparticulate of claim 16, wherein said graphite or carbon material isselected from polymeric carbon, amorphous carbon, chemical vapordeposition carbon, coal tar pitch, petroleum pitch, meso-phase pitch,carbon black, coke, acetylene black, activated carbon, fine expandedgraphite particle with a dimension smaller than 100 nm, artificialgraphite particle, natural graphite particle, or a combination thereof.18. The particulate of claim 1, wherein said ultrahigh molecular weightpolymer contains an electrically conductive material dispersed therein.19. The particulate of claim 18, wherein said electrically conductingmaterial is selected from an electron-conducting polymer, a metalparticle or wire, a graphene sheet, a carbon fiber, a graphite fiber, acarbon nano-fiber, a graphite nano-fiber, a carbon nanotube, a graphiteparticle, an expanded graphite flake, an acetylene black particle, andcombinations thereof.
 20. The particulate of claim 19, wherein saidelectrically conducting material has a thickness or diameter less than100 nm.
 21. The particulate of claim 1, wherein one or a plurality ofsaid particles is coated with a layer of carbon or graphene.
 22. Theparticulate of claim 1, wherein said positive electrode active materialis in a form of nano particle, nano wire, nano fiber, nano tube, nanosheet, nano belt, nano ribbon, nano disc, nano platelet, or nano hornand wherein said positive electrode active nano material having athickness or diameter from 0.5 nm to 100 nm.
 23. The particulate ofclaim 22, wherein said nano particle, nano wire, nano fiber, nano tube,nano sheet, nano belt, nano ribbon, nano disc, nano platelet, or nanohorn is coated with or embraced by a conductive protective coatingselected from a carbon material, graphene, electronically conductivepolymer, conductive metal oxide, or conductive metal coating.
 24. Theparticulate of claim 1, wherein said positive electrode active materialis selected from an inorganic material, an organic material, a polymericmaterial, or a combination thereof, and said inorganic material does notinclude sulfur or alkali metal polysulfide.
 25. The particulate of claim24, wherein said inorganic material is selected from a lithium cobaltoxide, lithium nickel oxide, lithium manganese oxide, lithium vanadiumoxide, lithium-mixed transition metal oxide, lithium iron phosphate,lithium manganese phosphate, lithium vanadium phosphate, lithium mixedmetal phosphate, lithium metal silicide, and combinations thereof. 26.The particulate of claim 24, wherein said inorganic material is selectedfrom a metal fluoride or metal chloride including the group consistingof CoF₃, MnF₃, FeF₃, VF₃, VOF₃, TiF₃, BiF₃, NiF₂, FeF₂, CuF₂, CuF, SnF₂,AgF, CuCl₂, FeCl₃, MnCl₂, and combinations thereof.
 27. The particulateof claim 24, wherein said inorganic material is selected from a lithiumtransition metal silicate, denoted as Li₂MSiO₄ or Li₂Ma_(x)Mb_(y)SiO₄,wherein M and Ma are selected from Fe, Mn, Co, Ni, V, and VO; Mb isselected from Fe, Mn, Co, Ni, V, Ti, Al, B, Sn, and Bi; and x+y≤1. 28.The particulate of claim 24, wherein said inorganic material is selectedfrom a transition metal dichalcogenide, a transition metaltrichalcogenide, or a combination thereof.
 29. The particulate of claim24, wherein said inorganic material is selected from TiS₂, TaS₂, MoS₂,NbSe₃, MnO₂, CoO₂, an iron oxide, a vanadium oxide, or a combinationthereof.
 30. The particulate of claim 24, wherein said organic materialcontains a phthalocyanine compound selected from copper phthalocyanine,zinc phthalocyanine, tin phthalocyanine, iron phthalocyanine, leadphthalocyanine, nickel phthalocyanine, vanadyl phthalocyanine,fluorochromium phthalocyanine, magnesium phthalocyanine, manganousphthalocyanine, dilithium phthalocyanine, aluminum phthalocyaninechloride, cadmium phthalocyanine, chlorogallium phthalocyanine, cobaltphthalocyanine, silver phthalocyanine, a metal-free phthalocyanine, achemical derivative thereof, or a combination thereof.
 31. Theparticulate of claim 24, wherein said organic material or polymericmaterial is selected from poly(anthraquinonyl sulfide) (PAQS), a lithiumoxocarbon, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),poly(anthraquinonyl sulfide), pyrene-4,5,9,10-tetraone (PYT),polymer-bound PYT, quino(triazene), redox-active organic material,tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE),2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), poly(5-amino-1,4-dyhydroxyanthraquinone) (PADAQ), phosphazene disulfide polymer, lithiated1,4,5,8-naphthalenetetraol formaldehyde polymer, hexaazatrinaphtylene(HATN), hexaazatriphenylene hexacarbonitrile (HAT(CN)₆), 5-benzylidenehydantoin, isatine lithium salt, pyromellitic diimide lithium salt,tetrahydroxy-p-benzoquinone derivatives (THQLi₄),N,N′-diphenyl-2,3,5,6-tetraketopiperazine (PHP),N,N′-diallyl-2,3,5,6-tetraketopiperazine (AP),N,N′-dipropyl-2,3,5,6-tetraketopiperazine (PRP), a thioether polymer, aquinone compound, 1,4-benzoquinone, 5,7,12,14-pentacenetetrone (PT),5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ),5-amino-1,4-dyhydroxy anthraquinone (ADAM), calixquinone, Li₄C₆O₆,Li₂C₆O₆, Li₆C₆O₆, or a combination thereof.
 32. The particulate of claim31, wherein said thioether polymer is selected frompoly[methanetetryl-tetra(thiomethylene)] (PMTTM),poly(2,4-dithiopentanylene) (PDTP), a polymer containingpoly(ethene-1,1,2,2-tetrathiol) (PETT) as a main-chain thioetherpolymers, a side-chain thioether polymer having a main-chain consistingof conjugating aromatic moieties and having a thioether side chain as apendant, poly(2-phenyl-1,3-dithiolane) (PPDT),poly(1,4-di(1,3-dithiolan-2-yl)benzene) (PDDTB),poly(tetrahydrobenzodithiophene) (PTHBDT),poly[1,2,4,5-tetrakis(propylthio)benzene] (PTKPTB), orpoly[3,4(ethylenedithio)thiophene] (PEDTT).
 33. The particulate of claim24, wherein said inorganic material is selected from a transition metaloxide, metal phosphate, metal silicide, metal selenide, transition metalsulfide, and combinations thereof.
 34. The particulate of claim 33,wherein said transition metal oxide contains a vanadium oxide selectedfrom the group consisting of VO₂, Li_(x)VO₂, V₂O₅, Li_(x)V₂O₅, V₃O₈,Li_(x)V₃O₈, Li_(x)V₃O₇, V₄O₉, Li_(x)V₄O₉, V₆O₁₃, Li_(x)V₆O₁₃, theirdoped versions, their derivatives, and combinations thereof, wherein0.1<x<5.
 35. The particulate of claim 33, wherein said transition metaloxide or metal phosphate is selected from a layered compound LiMO₂,spinel compound LiM₂O₄, olivine compound LiMPO₄, silicate compoundLi₂MSiO₄, tavorite compound LiMPO₄F, borate compound LiMBO₃, or acombination thereof, wherein M is a transition metal or a mixture ofmultiple transition metals.
 36. The particulate of claim 33, whereinsaid inorganic material is selected from: (a) bismuth selenide orbismuth telluride, (b) transition metal dichalcogenide ortrichalcogenide, (c) sulfide, selenide, or telluride of niobium,zirconium, molybdenum, hafnium, tantalum, tungsten, titanium, cobalt,manganese, iron, nickel, or a transition metal; (d) boron nitride, or(e) a combination thereof.
 37. A positive electrode active materiallayer containing multiple particulates of claim 1, an optionalconductive additive, and an optional binder that bonds said multipleparticulates together.
 38. A lithium battery containing an optionalanode current collector, an anode active material layer, a positiveelectrode active material layer as defined in claim 37, an optionalpositive electrode current collector, an electrolyte in ionic contactwith said anode active material layer and said positive electrode activematerial layer, and an optional porous separator.
 39. The lithiumbattery of claim 38, which is a lithium-ion battery or lithium metalbattery wherein the anode active material layer includes a lithium metalor an alloy of lithium metal.